ABSTRACT Closely related and co‐occurring species offer valuable systems to assess whether dispersal barriers in shared environments are navigated in a consistent manner. Labidiaster radiosus and L. annulatus have been morphologically described as two separate species from southern South America and the Southern Ocean respectively, yet the phylogenetic relationships and boundaries between these species have still not been genetically clarified. Labidiaster annulatus has pelagic larvae; however, the developmental mode for L. radiosus has not been confirmed. This study aimed to employ genetic methods to analyze the phylogeny, distribution, species boundaries, population structure, demographic history and genetic connectivity for L. radiosus and L. annulatus . Two molecular markers were sequenced in this study including a part of the mitochondrial gene cytochrome c oxidase subunit I (COI) and the intron of the nuclear adenosine triphosphate synthetase, beta subunit gene (ATPSβ—intron 7). A sister‐species relationship was revealed between L. radiosus and L. annulatus ; both species displayed circum‐Antarctic distributions, extending their known distributions and were found to co‐occur at Heard, Balleny and Scott Islands. Labidiaster radiosus and L. annulatus were estimated to have diverged ~3.56 mya (HPD95: 5.25–2.15). Additionally, L. radiosus was confirmed to have pelagic larvae in the Southern Ocean. Labidiaster radiosus population structure revealed clear subclades north and south of the APF, which diverged ~2.08 mya (HPD95: 3.48–0.58). Analyses for Labidiaster annulatus indicated high genetic connectivity among all locations across the Southern Ocean. Historical dispersal analyses showed high genetic connectivity among Scotia Sea Islands, and the South Sandwich Islands were identified as a possible contemporary sink population. Despite their similarities in life history and circum‐Antarctic distribution, L. radiosus and L. annulatus revealed contrasting population structures. This highlights the unpredictable nature of dispersal for Southern Ocean benthic invertebrates when based on life history alone.
Rodewald et al. (Wed,) studied this question.